Retinoblastoma, an intraocular neoplasm of infancy, presents with multifocal, usually bilateral, disease in 30% of affected individuals. Patients with bilateral disease, who are commonly cured from their eye tumor, transmit the so-called "retinoblastoma gene" in an autosomal dominant fashion to their offspring so that the gene pool for this disease is increasing. A marked increased incidence of second sarcomatous malignancy is also present in these individuals. Our in vitro studies will provide a better understanding of the genetic defect in hereditary retinoblastoma. Cultured fibroblasts from children with hereditary retinoblastoma will be tested for altered sensitivity, as measured by viability, to several types of DNA damaging agents, compared to appropriate control cells. The specific DNA damaging agents to be used include gamma radiation, actinomycin D, and mitomycin C; collectively, these agents cause a broad range of DNA damage as well as represent classes of DNA damaging agents to which retinoblastoma patients can be exposed as part of their therapy for their primary neoplasm. Because increased sensitivity to a specific DNA damaging agent in cultured cells suggests an inherent deficiency in the ability to repair DNA damage, hereditary retinoblastoma cells found to be sensitive to a specific DNA damaging agent will be studied for their ability to repair several types of DNA damage which may have resulted from exposure to the specific agent in question. The results of these studies will elucidate the genetic defect in hereditary retinoblastoma; the question of whether or not the defect represents an inability to handle certain types of DNA damaging agents will be answered. Future studies could then be directed at identifying the specific molecular defect. Furthermore, the improved developed techniques could be used to effectively identify "silent" carriers of the disease. The results of the studies will also shed light on the biologic heterogeneity of hereditary retinoblastoma and will help establish retinoblastoma as an important model for studying the hereditary aspects of malignancy.